The present invention relates generally to a semiconductor device and a method of manufacturing the same, and more particularly to improving reliability of connection between solder balls and a wiring substrate in a Ball Grid Array (BGA) type semiconductor device.
Recently, a technology is required for mounting and coupling a semiconductor package having a large number of connecting terminals onto a wiring substrate which becomes a mother board. To cope with such requirement, a Ball Grid Array (BGA) type package is practically used in which a large number of solder balls are disposed in a grid like arrangement on connecting terminals. A basic structure of the BGA type package is as follows. That is, in the BGA type package, a semiconductor chip is mounted on the face surface of a double-sided wiring substrate and solder balls are formed on the backside surface of the double-sided wiring substrate. On the face surface of the double-sided wiring substrate, there are formed electrode patterns which are electrically coupled with electrodes of the semiconductor chip. On the backside surface of the double-sided wiring substrate, there are formed conductive land portions which are electrically coupled with the electrode patterns on the face side and to which the solder balls are joined.
Japanese patent laid-open publication No. 10-98045 discloses an example of such BGA type package. In the structure disclosed in Japanese patent laid-open publication No. 10-98045, solder balls are joined onto land portions which are formed on a substrate and which are exposed via a solder resist layer. Thereafter, resin material for reinforcement is applied around a root portion of each of the solder balls.
However, the structure of Japanese patent laid-open publication No. 10-98045 has the following problems. That is, when the resin material for reinforcement is applied, it is necessary to selectively form a mask resin layer on the top portion of each solder ball, in order to prevent the resin material for reinforcement from attaching to the top portion of each solder ball. Here, the mask resin layer is made of a material which does not have affinity with the resin material for reinforcement. Further, it is also required that, after forming the resin material for reinforcement, the mask resin layer is removed. Therefore, a manufacturing process becomes complicated, and manufacturing costs are increased.
Therefore, it is an object of the present invention to obviate the disadvantages of the conventional semiconductor device and of the conventional method of manufacturing the semiconductor device.
It is another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which reliability of connection between solder balls and a wiring substrate can be improved.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which reliability of connection between solder balls and a wiring substrate can be improved without increasing the number of manufacturing process steps and manufacturing costs.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which resin portions for reinforcing the connection between the solder balls and the wiring substrate can be formed easily.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which resin portions for reinforcing the connection between the solder balls and the wiring substrate can be formed, without increasing the number of manufacturing process steps and manufacturing costs.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which resin portions for reinforcing the connection between the solder balls and the wiring substrate can be formed, without forming a mask resin layer on the top portion of each solder ball.
In the present invention, a reinforcement resin film is formed in the peripheral portion of each of conductive land portions on a substrate for coupling solder balls thereto, before the process of coupling the solder balls to the substrate of a semiconductor device. In the process of coupling the solder balls to the substrate of the semiconductor device, a portion of the reinforcement resin film is pushed away from each of the conductive land portions by the material of the solder ball which is melted by heating. In the present invention, the reinforcement resin film is formed by utilizing this phenomenon. As a result, both a process of previously forming a mask layer on the solder balls and a process of removing the mask layer become unnecessary.
The reinforcement resin film formed in this way surrounds each of the root portions of the solder balls, and is bent at an inner area thereof. The bent portion of the reinforcement resin film pushes the root portion of each of the solder balls by restitutive force or elastic force. Thereby, coupling between the solder balls and the conductive land portions can be reinforced. Even if a stress such as a shearing stress is applied to an interface portion between each of the solder balls and the substrate, it is possible to absorb or disperse such stress into the material of the reinforcement resin film. Also, in the semiconductor device fabricated in this way, a quantity of material for the reinforcement resin film can be minimum, and does not affect the costs of the semiconductor device. Further, when the semiconductor device is mounted on a mother board and the like, the reinforcement resin film does not become a hindrance to the mounting of the semiconductor device.
According to an aspect of the present invention, there is provided a semiconductor device comprising: a wiring substrate; a semiconductor element mounted on a first surface of the wiring substrate; a plurality of conductive land portions exposed respectively via openings of an insulating material portion of a second surface of the wiring substrate which is opposite to the first surface; a plurality of solder balls respectively joined to the plurality of conductive land portions; and a plurality of reinforcement resin film portions for reinforcing coupling between the solder balls and the conductive land portions, each of the reinforcement resin film portions being formed around a portion of the solder ball joining to the conductive land portion, and each of the reinforcement resin film portions being bent to form a portion along the wiring substrate and a portion along the side surface of the solder ball.
In this case, it is preferable that coupling between the solder balls and the conductive land portions is reinforced by elastic force of the bent portions of the reinforcement resin film portions.
It is also preferable that the plurality of conductive land portions are electrically coupled with electrodes of the semiconductor element.
It is further preferable that each of the reinforcement resin film portions has a structure in which an inner circumferential portion of a ring shaped film having a uniform thickness is pushed and bent away from the conductive land portion.
It is advantageous that the surface of the conductive land portion is recessed from a surface portion of the second surface of the wiring substrate at the peripheral portion of the conductive land portion.
It is also advantageous that the reinforcement resin film portions are made of silicone resin.
It is further advantageous that the wiring substrate is a flexible wiring substrate in which a conductive wiring pattern layer is sandwiched by insulating layers.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising: preparing a semiconductor element; preparing a wiring substrate, the wiring substrate having a first surface on which the semiconductor element is to be mounted and a second surface opposite to the first surface, wherein a plurality of conductive land portions being exposed respectively via openings of an insulating material portion of the second surface of the wiring substrate; mounting the semiconductor element on the first surface of the wiring substrate; forming a plurality of reinforcement resin film portions on the second surface of the wiring substrate, each of the reinforcement resin film portions having an opening portion, each of the reinforcement resin film portions partially overlapping a corresponding one of the conductive land portions, and a portion of each of the conductive land portions being exposed via the opening portion of the corresponding one of the reinforcement resin film portions; disposing solder balls respectively on the conductive land portions which expose via the opening portions of the reinforcement resin film portions, and heating and melting the solder balls, the portions of the reinforcement resin film portions which overlap the conductive land portions being pushed away from the conductive land portions; and cooling and curing the melted solder balls.
In this case, it is preferable that, after the cooling and curing the melted solder balls, coupling between the solder balls and the conductive land portions is reinforced by the reinforcement resin film portions.
It is also preferable that each of the conductive land portions has a circle shape, each of the opening portions of the reinforcement resin film portions has a circle shape, the center of each of the conductive land portions substantially conforms to the center of the corresponding one of the reinforcement resin film portions, and the diameter of each of the conductive land portions is larger than the diameter of the corresponding one of the opening portions of the reinforcement resin film portions.
It is further preferable that the forming a plurality of reinforcement resin film portions on the second surface of the wiring substrate is performed by using a screen printing method, before the disposing solder balls respectively on the conductive land portions which expose via the opening portions of the reinforcement resin film portions and heating and melting the solder balls.
It is advantageous that the reinforcement resin film portions are made of silicone resin.
It is also advantageous that a gap is formed between each of the portions of the reinforcement resin film portions which overlap the conductive land portions and the corresponding one of the conductive land portions.
It is further advantageous that the surface of each of the conductive land portions is recessed from the surface portion of the wiring substrate at the peripheral portion of the corresponding one of the conductive land portions, thereby a gap is formed between each of the portions of the reinforcement resin film portions which overlap the conductive land portions and the corresponding one of the conductive land portions.
It is preferable that, in the disposing solder balls respectively on the conductive land portions which expose via the opening portions of the reinforcement resin film portions and heating and melting the solder balls, material of each of the melted solder balls enters into the gap, and the portions of the reinforcement resin film portions which overlap the conductive land portions being pushed away from the conductive land portions.
It is also preferable that, in the forming a plurality of reinforcement resin film portions on the second surface of the wiring substrate, the reinforcement resin film portions having substantially uniform thickness are formed.
It is further preferable that the diameter of each of the opening portions of the reinforcement resin film portions is smaller than the diameter of the corresponding one of the solder balls.
It is advantageous that the diameter of each of the opening portions of the reinforcement resin film portions is 50-80% of the diameter of the corresponding one of the solder balls.
It is also advantageous that the width of each of the portions of the reinforcement resin film portions which overlap the conductive land portions is approximately 10% of the diameter of the corresponding one of the solder balls.
It is further advantageous that each of the reinforcement resin film portions has a circle shape and has the opening portion at the center thereof, and the diameter of each of the reinforcement resin film portions is larger than the diameter of the corresponding one of the solder balls and is smaller than twice of the diameter of the corresponding one of the solder balls.